Compressor

ABSTRACT

A screw-type compressor ( 10 ) for compressing refrigerant, which comprises: an electric motor ( 14 ), which has a rotor ( 16 ) and a stator ( 18 ); a drive shaft ( 20 ); and a compressing device ( 22 ) having a compressor screw ( 24 ); wherein the compressor screw ( 24 ) and the rotor ( 16 ) of the electric motor ( 14 ) are arranged against or on the drive shaft ( 20 ), wherein the drive shaft ( 20 ) is rotatably supported by a first, a second, and a third radial bearing ( 27, 28, 30 ), wherein the first radial bearing ( 27 ) is arranged between the rotor ( 16 ) of the electric motor ( 14 ) and the compressor screw ( 24 ), wherein the second radial bearing ( 28 ) is arranged on a side of the compressor screw ( 24 ) opposite the first radial bearing ( 27 ), and wherein the third radial bearing ( 30 ) is arranged on a side of the rotor ( 16 ) of the electric motor ( 14 ) opposite the first radial bearing ( 27 ), wherein the first radial bearing and the second radial bearing are both designed as rolling-element bearings, and the third radial bearing ( 30 ) is designed as a plain bearing.

The present invention relates to a screw compressor according to the preamble of claim 1.

Screw compressors of this kind are used in many applications, since their construction is robust and the achievable efficiency is high. An electric motor is in most cases used as drive device for the actual compression device which, for example, has two compressor screws or screw rotors engaging in each other.

The motors of the above-described compressors, which can be designed for example as semi-hermetic compact screw compressors, are in most cases mounted in an overhung configuration. In the compressors of this kind, the compressor rotor, i.e. a first compressor screw, and the motor rotor, i.e. the rotor of the electric motor, are arranged on a common shaft (drive shaft) which has two radial bearing points. A first radial bearing point is arranged at the compressor-side end of the shaft, and a second radial bearing point is located on the shaft portion between the compressor rotor and the motor rotor. That is to say, a bearing of the drive shaft or of the rotor of the motor is present only on one side of the motor. A disadvantage of this is that, with the increasing compressor dimensions and with the increasing motor speed, resonance can occur, which can lead to the motor rotor running on the motor stator.

In order to avoid damage being caused by this, a compressor is set forth in EP 1 348 077 A1 having a third radial bearing point in the form of a rolling bearing on the motor-side end of the shaft. The motor of the compressor is thus mounted at both sides by means of rolling bearings. However, on account of the three bearing points, there is an overdetermination of the position of the drive shaft, which can only be compensated if the portion of the drive shaft located between the first radial bearing and the third radial bearing is designed to compensate alignment errors arising between the radial bearings. This is achieved by a flexurally elastic portion of the drive shaft.

The above-described construction requires considerable effort in terms of design and manufacturing technology.

Proceeding from this, the object of the present invention is to make available a compressor which prevents a collision between rotor and stator of the motor and which at the same time can be realized in a simple and cost-effective manner.

This object is achieved by a compressor having the features of claim 1.

Accordingly, the object is achieved by a screw compressor for compressing refrigerant, which comprises an electric motor, with a rotor and a stator, and also a drive shaft and a compressing device having (at least) a compressor screw or (at least) a screw rotor, wherein the compressor screw and the rotor of the electric motor are arranged against or on the drive shaft. The drive shaft is rotatably mounted by means of a first, a second and a third radial bearing, and the first radial bearing is arranged between the rotor of the electric motor and the compressor screw. The second radial bearing is arranged on a side of the compressor screw opposite the first radial bearing, and the third radial bearing is arranged on a side of the rotor of the electric motor opposite the first radial bearing. The first radial bearing and the second radial bearing are both designed as rolling bearings, and the third radial bearing is designed as a plain bearing.

The design of the third bearing as a plain bearing ensures a suitable play on the bearing point itself, such that the positional overdetermination of the drive shaft, which is caused by the latter being supported at three points, can be compensated without an additional flexural elasticity of the drive shaft or without any other compensating measures, while the two rolling bearings ensure a positionally precise support of the drive shaft.

Further optional features of the invention are set forth in the dependent claims and in the following description of the figures. The described features can in each case be realized individually or in any desired combinations. Accordingly, the invention is described below with reference to the appended drawings and on the basis of illustrative embodiments. In the drawings:

FIG. 1 shows a sectional view of an illustrative embodiment of a compressor according to the invention; and

FIG. 2 shows an enlarged view of a partial area of the compressor according to FIG. 1.

FIG. 1 shows a possible embodiment of a compressor according to the invention, more specifically of a screw compressor 10 according to the invention, which is also referred to below for short as compressor 10. The compressor 10 has a housing 12, and an electric motor 14 arranged in the housing 12. The electric motor 14 has a rotor 16 and a stator 18. Moreover, the screw compressor 10 has a drive shaft 20, and a compressing device 22 with a first compressor screw and second compressor screw engaging in each other, or with a first screw rotor 24 and second screw rotor 26 engaging in each other, wherein the first compressor screw 24 and the rotor 16 of the electric motor 14 are arranged against or on the drive shaft 20. Accordingly, the drive shaft 20 is driven in rotation by the electric motor 14 and at the same time drives the compressing device 22. In alternative embodiments, the compressor according to the invention can have just one compressor screw 24 or else three, or more than three, compressor screws.

The drive shaft 20 is rotatably mounted in the compressor 10 by means of a first, a second and a third radial bearing 27, 28 and 30, wherein the first radial bearing 27 is arranged between the rotor 16 of the electric motor 12 and the first compressor screw 24. The second radial bearing 28 is arranged on a side of the first compressor screw 24 opposite the first radial bearing 27, and the third radial bearing 30 is arranged on a side of the rotor 16 of the electric motor 12 opposite the first radial bearing 27. While the first radial bearing 27 and the second radial bearing 28 are designed as rolling bearings, the third radial bearing is designed as a plain bearing (here as a plain bearing with fluid friction or a hydrodynamic plain bearing, but in alternative embodiments also as a dry-running plain bearing). It will be noted here that a hydrodynamic plain bearing is also suitable for damping shaft movements and therefore also, and in particular, for damping vibrations.

The third radial bearing 30, also designated below as plain bearing 30, communicates with a lubricant inlet 32, in the form of an oil delivery channel, and with a lubricant outlet 34, in the form of an oil return channel. The lubricant inlet 32 moreover communicates with a first volume (oil distribution chamber (not shown in the figures)) which can be subjected to a first pressure, in the possible embodiment described here with a compression end pressure of the compressor.

Moreover, the lubricant outlet 34 communicates with a second volume (not shown in the figures) which can be subjected to a second pressure, in the possible embodiment described here with approximately a suction pressure of the compressor 10. In the described embodiment, the second volume is a closed compression work chamber of the compressor 10, i.e. the work chamber of the compressor 10 where the suction process is already completed and the compression process has just begun. In this work chamber, the pressure is almost equal to the suction pressure.

This construction ensures that lubricant is delivered at a relatively high pressure, such that the bearing is as good as possible and free of friction, i.e. with a substantially closed lubricant film between the plain bearing 30 and the drive shaft 20. Subjecting the lubricant outlet 34 to a relatively low pressure ensures a reliable discharge of the lubricant which, in the presently described embodiment, is formed by the oil that the compressor 10 also uses as lubricant.

The plain bearing 30 is arranged in a bearing bushing 36, which is arranged at least partially in the housing 12. The bearing bushing 36 is arranged parallel and concentric to the drive shaft 20. The bearing bushing 36 has a first end 38, through which the drive shaft 20 extends, and a second end 40, which lies opposite the first end 38.

The bearing bushing 36 is sealed off from the environment, i.e. the interior of the housing 12, both at its first end 38 and at its second end 40, wherein the seal at the first end 38, through which the drive shaft 20 extends, is embodied by means of a first cover 42, which has a drive shaft passage 44 and a radial shaft seal 46. A second cover 48 is arranged at the second end 40 for sealing purposes and, if appropriate, is mounted on the second end 40 using suitable sealing materials.

However, as an alternative to this, the second end can also have, for example, a closed design, i.e. the bearing bushing 36 can alternatively be configured, for example, in the form of a blind hole or in the form of a cylinder closed at one end. In this way, the plain bearing 30 is sealed off from the environment, which has the effect that no lubricant can escape to the environment.

In order to collect the lubricant of the plain bearing and discharge the lubricant in a specific way, the compressor 10 has a lubricant collection chamber 50 which, in the presently described embodiment, is arranged inside the bearing bushing 36 and which communicates with the lubricant outlet 34. The lubricant collection chamber is fluidically connected to the plain bearing 30 or open with respect to the plain bearing 30, so as to be able to take up lubricant of the plain bearing 30 in an unimpeded manner, while being sealed off from the environment analogously to the plain bearing 30.

The sealing with respect to the environment is provided, in the same way as for the plain bearing 30, by the first cover 42 and also the radial shaft seal 46 and the second cover 48. The lubricant collection chamber 50 is accordingly delimited by an inner wall 52 of the bearing bushing 36 and by the first and second covers 42, 48, which are arranged at the radial ends of the bearing bushing 36. In alternative embodiments, the lubricant collection chamber 50 can also be arranged outside the bearing bushing 36 and can be connected to the plain bearing 30, for example via a channel.

The use of the plain bearing 30 with fluid friction ensures the least possible formation of heat in the area of the bearing point. By additional configuration of a lubricant collection chamber 50, which communicates with the plain bearing (fluidic connection, fluidic communication), the lubricant can additionally be collected in a targeted way. By virtue of the fact that the plain bearing 30 and the lubricant collection chamber 50 are arranged sealed off from the environment, and as a result of the targeted discharge of the lubricant, there is no bearing-induced introduction of lubricant into the suction stream of the compressor 10. The pressurized delivery of lubricant leads to the best possible lubricating action and therefore to a further reduced development of heat.

Although the invention has been described on the basis of embodiments with fixed combinations of features, it nonetheless also encompasses the conceivable further advantageous combinations as are indicated in particular, but not exhaustively, by the dependent claims. All of the features disclosed in the application documents are claimed as essential to the invention insofar as they are novel over the prior art, whether individually or in combination.

LIST OF REFERENCE SIGNS

-   10 compressor -   12 housing -   14 electric motor -   16 rotor -   18 stator -   20 drive shaft -   22 compressing device -   24 first compressor screw -   26 second compressor screw -   27 first radial bearing -   28 second radial bearing -   30 third radial bearing -   32 lubricant inlet -   34 lubricant outlet -   36 bearing bushing -   38 first end of the bearing bushing 36 -   40 second end of the bearing bushing 36 -   42 first cover -   44 drive shaft passage -   46 radial shaft seal -   48 second cover -   50 lubricant collection chamber -   52 inner wall of the bearing bushing 36 

1. A screw compressor for compressing refrigerant, comprising an electric motor, which has a rotor and a stator, and also a drive shaft and a compressing device with a compressor screw, wherein the compressor screw and the rotor of the electric motor are arranged against or on the drive shaft, wherein the drive shaft is rotatably mounted by means of a first, a second and a third radial bearing, wherein the first radial bearing is arranged between the rotor of the electric motor and the compressor screw, wherein the second radial bearing is arranged on a side of the compressor screw opposite the first radial bearing, and wherein the third radial bearing is arranged on a side of the rotor of the electric motor opposite the first radial bearing, wherein the first radial bearing and the second radial bearing are each designed as rolling bearings, and the third radial bearing is designed as a plain bearing.
 2. The compressor as claimed in claim 1, wherein the plain bearing communicates with a lubricant inlet and with a lubricant outlet, wherein the lubricant inlet communicates with a first volume which can be subjected to a first pressure, in particular for example a compression end pressure of the compressor, and/or the lubricant outlet communicates with a second volume which can be subjected to a second pressure, in particular for example a suction pressure of the compressor.
 3. The compressor as claimed in claim 2, wherein the lubricant outlet communicates with a closed compression work chamber.
 4. The compressor as claimed in claim 1, wherein the compressor has a lubricant collection chamber for lubricant of the plain bearing.
 5. The compressor as claimed in claim 4, wherein the lubricant collection chamber communicates with a lubricant outlet
 6. The compressor as claimed in claim 1, wherein the plain bearing and the lubricant collection chamber are sealed off from the environment.
 7. The compressor as claimed in claim 1, wherein the plain bearing is arranged in a bearing bushing which has a first end, through which the drive shaft extends, and a second end, wherein the bearing bushing is sealed off from the environment both at its first end and at its second end, wherein the seal at the first end, through which the drive shaft extends, is embodied by means of a first cover, which has a drive shaft passage and a radial shaft seal.
 8. The compressor as claimed in claim 4, wherein the lubricant collection chamber is delimited by an inner wall of a bearing bushing and by a first and second cover, which are arranged at radial ends of the bearing bushing.
 9. The compressor as claimed in claim 1, wherein the plain bearing, in particular for damping vibrations, is designed as a hydrodynamic plain bearing. 